Risk Assessment Tool (RAT)
Questions about the RATs?
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The cancer Risk Assessment Tool (RAT) is an algorithm that can be used to calculate the absolute risk that a patient has an undiagnosed cancer based on certain risk factors and their current symptoms.
The RATs are designed to support GP decision making when deciding which patients require further investigation or referral. The RAT does not replace clinical judgement, but gives more information on which to base patient management decisions.
The RAT tool estimates separate risk values for certain cancer types, based on the positive predictive value* (PPV) of symptoms. Risk can be read for a single symptom or for a combination of the two worst symptoms a patient presents with. The tool also provides the risk associated with a patient presenting the same symptom more than once in a 12 month period.
The colours used in the cells of the tool depict risk values ranges:
- <1% = white
- 1-2% = yellow
- 2-5% = orange
- >5% = red
The current 2015 NICE referral guidelines for suspected cancer referral suggest referral at a threshold of 3% and above. Although the colour code and associated risk values may help support referral decision making, these should not replace clinical judgement and experience.
RATs are currently available for 15 cancer types.
*The chance of a patient having the disease of interest when presenting with a particular symptom(s). E.g. based on the lung RAT, a person reporting haemoptysis has a 2.4% chance of the symptom being due to an underlying lung cancer.
The RATs were developed using a mix of population based case-control studies and electronic cohort studies. These studies were collectively known as the ‘Cancer Prediction in Exeter’ (CAPER) studies, which aimed to quantify the risk of a particular type of cancer, based on a given symptom, either independently or in combination with others.
The studies benefit from having relatively large sample sizes. The main limitation is the reliance on symptoms recorded at practice level via READ codes, which may be recorded differently by different GPs.
See the research underpinning each RAT:
An evaluation of lung and colorectal desk-based RATs published in 2013, which suggested that using RATs in a cohort of over 600 GPs from 7 former English Cancer Networks led to increased cancer investigations, urgent referrals and cancer diagnoses.
The results are encouraging but it is not possible to assess the extent to which using the RATs were responsible for the changes seen in the study. Further research could help determine its impact, but this is challenging given the rollout of different algorithms and a range of other activities within the early diagnosis sphere.
In a separate interview study with around 20 GPs most found desk-based RATs useful in supporting clinical decision making without superseding clinical judgement. However, as part of the study, practices were supported and provided with training by cancer network staff which may have impacted on acceptability of the tools.
In a similar interview study offering adequate training alongside the implementation of the tool was highlighted as a key factor for successful implementation. And although the tool was felt to increase GP awareness of cancer as a potential diagnosis, concerns about ‘prompt fatigue’ were also raised.
This replaces the desk easel format previously available.
GP computer system integration
A number of GP software providers have integrated the cancer RAT into software known as electronic Cancer Decision Support (eCDS) in order to provide easier access to it.